“Word is they’ve quietly gone out a bunch of times since late summer, and the out-of-left-field relationship is sure to shock everyone, especially Jen,” a source revealed. “Pals think they’re really starting to develop feelings for each other.”

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As Life & Style previously reported, Angelina arranged for the pair to meet up at Justin’s favorite NYC restaurant in August under the pretense of talking about a movie role. “Since that night, their relationship has only grown in momentum and intensity,” the source claimed, adding that at this point, “friends wouldn’t be surprised if they’re sending steamy texts and having secret sleepovers.”

Despite maintaining a low profile thus far, the source noted that Angelina doesn’t have any issue with going public. “It’s not like Angie is worried about the romance getting out,” they said. “The reality is that they’re really into each other,” the source added. “They can talk for hours on end.”

As it stands, the source confirmed that both Jennifer and Angelina’s ex-husband Brad Pitt are unaware of her romance with Justin — but it’s only a matter of time before it all blows up in their faces.

“I don’t care how much chemistry Angie and Justin have, what they’re doing to Jen is just plain cruel,” says the insider. “She’ll be devastated when she finds out. Can you imagine? The woman who wrecked your marriage to Brad is now dating your last ex-husband? Jen will be in tears,” the source confessed.

For more on this story, pick up the latest issue of Life & Style, on newsstands now.